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New Coordination Polymers Incorporating Rigid and Flexible Polypyrazolyl Ligands with Late Transition Metals. Microporosity, Thermal Resistance, Photoluminescence and Antibacterial Action
No full textThe interest in engineering and constructing coordination compounds with supramolecular structures has permanently increased during the last two decades. As a matter of fact, coordination polymers (CPs), also comprising metal-organic frameworks (MOFs), seem very promising in a variety of fields of industrial, technological and environmental relevance, e.g., as selective and reversible adsorbents of gases and/or volatile organic compounds, as highly efficient and selective catalysts, as magnetic and photoluminescent materials capable of both metal- and ligand-centered emission, or even as antimicrobial agents.\ud
Coordination polymers are generally formed by the self-assembly of metallic centres and bridging organic linkers. Diverse geometries of the metal ions coupled to sizeable, shapeable and functionalizable organic bridging linkers, may give birth to a huge and impressive class of CPs with various architectural topologies and capable to bring a lot of advantages in terms of regularity, designability and versatility.\ud
In Chapter 1 of this thesis, a background and main concepts about coordination polymers are presented. A review of some key advances in the field along with a discussion in terms of relationship between the nature and structure of specifically designed organic linkers and the properties of the products is also included. Practical examples demonstrate that the physical and chemical properties of the linkers play a decisive role in the properties of novel functional MOFs. One particular section of Chapter 1 was dedicated to state-of-the-art coordination frameworks incorporating the nitrogen ligand pyrazole and its derivatives, polypyrazoles. This section was included also to anticipate the work of this thesis about new coordination frameworks incorporating different rigid and flexible polypyrazolyl ligands. Their coordinative potentialities have been insistently explored due to the remarkable robustness of the corresponding supramolecular frameworks coupled to other interesting properties, making them suitable candidates as multifunctional materials. Another particular section was dedicated to a brief recall about silver(I) coordination polymers that have demonstrated, through the last two decades, interesting antimicrobial action against different cultures of bacteria, also anticipating the new silver(I)-based coordination polymers with antibacterial action covered in this thesis. An overview of microporous properties followed by an outline of this thesis end up Chapter 1.\ud
Chapter 2, dedicated to the experimental work of this thesis, presents the synthesis of forty three new coordination polymers based on five polypyrazolyl ligands as linkers and different late transition metals as connectors. Accordingly, three rigid ligands such as 4,4’-bipyrazole (H2BPZ), 3,3’,5,5’-tetramethyl-4,4’-bipyrazole (H2Me4BPZ) and 1,3,5-tris((4-pyrazol-1H-yl)phenyl)benzene ligand (H3BTPP), along with two flexible ones such as 1,4-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)benzene ligand (H2BDMPX) and 4,4'-bis((3,5-dimethyl-1H-pyrazol-4-yl)methyl)biphenyl (H2DFBDMP) have led, either by conventional paths or following solvothermal routes, to the isolation of coordination polymers of formula [M(BPZ)]∙Solv (M = Zn, 1; Co, 2; Cd, 3; Cu, 5; Ni, 6; Pd, 7; Solv = DMF, MeCN or H2O), [Ag2(BPZ)] (10) and [Ag(H2BPZ)(X)] (X = NO3, 11; ClO4, 12; BF4, 13; PF6, 14; CH3SO3, 15; CF3SO3, 16), [M(Me4BPZ)] (M = Zn, 17; Co, 18; Cd, 19), [Mx(OH)y(BTPP)z]∙Solv (x = 9, y = 12 and z = 2 for M = Ni, 20; x = 12, y = 18 and z = 2 for M = Cu, 21; x = 3, y = 0 and z = 2 for M = Co, 23; Solv = DMF and H2O), [Mx(BDMPX)] (x = 1 for M = Zn, 24; Co, 25; Cd, 26; x = 2 for M = Cu, 27), [Mx(DFBDMP)] (x = 1 for M = Zn, 33; Co, 34; Cd, 35; x = 2 for M = Cu, 36; Ag, 37), [Ag(H2BDMPX)(X)] (X = ClO4, 28; BF4, 29; NO3, 30; CF3CO2, 31; CF3SO3, 32), and [Ag(H2DFBDMP)(X)] (X = NO3, 38; ClO4, 39; BF4, 40; PF6, 41; CF3CO2, 42; CF3SO3, 43). Their structural characterization was done by means of infrared spectroscopy (IR), elemental analysis (EA), thermal gravimetric analysis (TGA) and, in some of the compounds, X-ray powder diffraction (XRPD) coupled to thermodiffractometric studies.\ud
Chapter 3, dedicated to results and discussion, show the most important results in view of potential applications. Section 3.1. describes the synthesis of the new coordination polymers, along with a spectroscopic characterization by infrared spectroscopy (IR), revealing the main absorption bands in their spectra. Section 3.2. reveals the molecular structures for some of the synthesized compounds by means of state-of-the-art laboratory powder diffraction methods, allowing to disclose diverse and fascinating architectures, some of them with porous structure, developed by the polypyrazolyl spacers when coordinated to different metal ions. Section 3.3. is dedicated to the thermal behaviour displayed by the new polymeric materials, highlighting in some of them a remarkable thermal robustness, peaking at 500 °C in the case of Cd(II) derivatives based on the rigid H2Me4BPZ and the flexible H2BDMPX and H2DFBDMP ligands. A certain framework flexibility in some of the synthesized PCPs, was also studied by means of thermodiffractometric techniques, highlighting, e.g., the permanent porosity of 1-3, 5 and 6, retained along consecutive temperature cycles in all these cases but 3. Species 24, 25, 33 and 34 reppresent a notable example of pro-porous materials, their adsorption performances implying a low-temperature opening of the rhombic motifs, stimulated by the gas probe and facilitated by the nature of the ligand. Prompted by the envisaged molecular structures containing pores, their adsorption properties with N2 at 77 K and CO2 at 298 K are presented in Section 3.4. When excited with an UV radiation, some of the polymeric species proved their photoluminescence properties, which are shown and discussed in Section 3.5. When embedded into polyethylene disks, the silver(I) coordination polymers 10, 11 and 13-16 based on the rigid H2BPZ ligand, demonstrated their activity as topical antibacterial agents against suspensions of E. coli, P. aeruginosa, and S. aureus: a complete reduction of the three bacterial strains is achieved in 24 h, the reduction of S. aureus reaching ca. 90% in only 2 h. The biocidal action was expressed also by contact susceptibility tests, as discussed in Section 3.6.\ud
Concluding remarks and future perspectives are given in Chapter 4. The Annexes section was added at the end of this thesis, including different IR spectra, some tables with crystallographic data, graphical results of the Rietveld refinements, thermodiffraction traces, an XRF plot and two SEM images. All these data were attached also as supplementary information in order to give the reader a more complete understanding of the experimental work presented throughout the thesis
Synthesis and physico-chemical properties of a novel series of aromatic electron acceptors based on N-heterocycles
No full textThe synthesis of a novel series of N-based heterocyclic salts using a simple and efficient N-alkylation of 1,2-bis(4-pyridyl)ethane with reactive halides is reported. These compounds can be transformed into the corresponding pyridinium methylides by addition of a base. The former exhibit an unstable absorption bands at 395-410 nm. The structures of the salts were fully characterized by UV-vis, IR, NMR and MS spectroscopy and elemental analysis. The pK values of selected compounds were also determined and the acid basic equilibrium was investigated by UV-vis spectrophotometry. The thermal stability of all species was determined by thermogravimetric analysis. (C) 2012 Elsevier Ltd. All rights reserved
Rigidity versus flexibility of the ligand upon the porosity degree of new metal-organic polymeric materials
No full textIn the context of the adsorption gas property, four metal-organic polymeric materials based on cobalt(II), palladium(II), nickel(II) and zinc(II) with the rigid 4,4'-bipyrazole (labeled as Co-bpz, Pd-bpz, Ni-bpz and Zn-bpz), and four polymeric materials based on cobalt(II) nitrate, cobalt(II) acetate, nickel(II) nitrate and copper(II) acetate with the flexible bis(1,2,4-triazolyl)methane (labeled as Co1-btm, Co2-btm, Ni-btm and Cu-btm) have been investigated toward N-2 adsorption at 77 K. Their porous nature is manifested by the following values of the Langmuir surface area: 1057 m(2)/g, 1035 m(2)/g, 962 m(2)/g and 866 m(2)/g for Co-bpz, Pd-bpz, Ni-bpz and Zn-bpz, respectively, whereas the values of the surface area for the btm-based materials are all null. These results show that the rigid 4,4'-bipyrazolyl ligand induces the formation of porous polymeric structures, whereas the flexible bis(1,2,4-triazolyl)methane ligand induces the formation of nonporous structures
Investigating the Structural Features and Spectroscopic Properties of Bis(tetrazolato)-Based Coordination Polymers
No full textThe luminescent compound xylene-bis(2H-tetrazol-5-yl) (H2BTZPX) was prepared and employed in the construction of the novel coordination polymers (CPs) Zn(BTZPX), Ag2(BTZPX), and Hg(BTZPX), containing d10 transition metal ions. Powder X-ray diffraction (PXRD) structure determination enabled us to disclose the crystal and molecular structure of the three CPs: while Zn(BTZPX) features a 3-D polymeric network, Ag2(BTZPX) and Hg(BTZPX) show 2-D corrugated layers. Thermogravimetric analysis and variable-temperature PXRD revealed the appreciable thermal robustness of the three CPs, peaking up to 370 °C, in air, in the case of Ag2(BTZPX). Given the sizable fluorescence emission of the ligand in the solid state, both H2BTZPX and the three CPs were characterized as to their electronic-state transition spectroscopic properties. UV–visible absorption unveiled a bathochromic shift for both the ligand and the CPs with respect to the absorption maximum of the main chromophore of the spacer, i.e., the benzene ring. In order to understand this peculiarity, quantum mechanical calculations were performed using the time-dependent density-functional theory approach. Furthermore, absorption spectra of H2BTZPX in different organic solvents were recorded. To investigate how the luminescence properties of H2BTZPX are influenced by complexation, the fluorescence emission spectra of H2BTZPX and the three CPs were recorded, and the fluorescence quantum yields determined by comparison to anthracene. Zn(BTZPX) exhibited enhanced fluorescence with respect to the ligand, while fluorescence was notably reduced for Ag2(BTZPX) and barely detectable for Hg(BTZPX). This occurrence suggests different decay pathways, which were further investigated by reconstructing the time-resolved fluorescence decays by means of time-correlated single-photon counting
Nickel(II) and copper(I,II)-based metal-organic frameworks incorporating an extended tris-pyrazolate linker
No full textSolvothermal reactions between the tritopic pyrazole-based ligand 1,3,5-tris((1H-pyrazol-4-yl)phenyl)benzene (H3BTPP) and nickel(ii) perchlorate or copper(ii) nitrate afforded two new metal-organic frameworks, Ni3(BTPP)2·solvent (Ni-BTPP) and CuI4CuII2(OH)2(BTPP)2·solvent (Cu-BTPP). Powder diffraction structure determination methods were employed to determine the crystal and molecular structure of the copper(i,ii) derivative: triangular [Cu3N6(μ3-OH)] nodes are connected to six nearby ones by the pyrazolate ligands, thus constructing flat two-dimensional layers that stack to form slit-like one-dimensional channels. Thermogravimetric analyses highlighted both the thermal stability and the permanent porosity of these two materials. Porosity was confirmed by N2 adsorption at 77 K, yielding Langmuir specific surface areas of 1923(3) m2 g-1 and 874(8) m2 g-1 for Ni-BTPP and Cu-BTPP, respectively. Additionally, Ni-BTPP adsorbed 1.73 mmol g-1 (7.6 wt%) of CO2 at the mild conditions of 298 K and 1 bar
1,3-Bis(1,2,4-triazolyl)adamantine-based Coordination Polymers
No full textThe hybrid organic-inorganic materials known as coordination polymers are continuously gaining ground of scientific research, especially due to the interesting and promising functionalities they possess, e.g. magnetic, optical, electrical, redox, and luminescence properties, as well as, when permanent porosity is present, gas adsorption or
separation, catalytic activity, and drug delivery. The reaction of the flexible ligand 1,3-bis(1,2,4-triazolyl)adamante (tr2ad, Scheme 1) with chlorides of different late transition metals, either following conventional routes or under solvothermal conditions, afforded the coordination polymers having the general stoechiometric formula of the type M(tr2ad)Cl2 (M = Zn,1; Cu, 2; Cd, 3; Ni, 4; Co, 5). Preliminary ab initio X-ray powder diffraction analyses revealed that 1 developes into a 1-D polymeric chain, while 2 features a 2-D polymeric structure. Thermal-gravimetric analyses (TGA) showed relevant thermal robustness of all these materials, peaking up to the onset of decomposition set at 350 °C
Dinuclear Arene Ruthenium(II) Complexes with 3,3’,5,5’-Tetramethyl-4,4’-Bipyrazole and Modulation of Proteasome Activity
No full textDuring the last decades, the preparation of half-sandwich ruthenium(II) complexes incorporating systems has registered a growing attention, especially due to their potentiality as metallo-pharmaceuticals1 as well as catalyst in synthetic organic chemistry.2 In the present work, a series of dinuclear arene ruthenium(II) complexes coordinated by the ditopic N-ligand 3,3’,5,5’-tetramethyl-4,4’-bipyrazole (H2Me4BPZ) have been prepared (Scheme 1), and preliminary results regarding their ability to modulate proteasome activity are reported
Unsolvated ruthenium(II) benzene dichloride: The beta polymorph
No full textA novel polymorph of the unsolvated species [Ru2(benzene)2Cl4] (beta form in the following) was serendipitously isolated as a polycrystalline powder. Its molecular and crystal structure was unraveled by means of state-of-the-art X-ray powder diffraction structure determination methods applied to laboratory data, and was compared to those of both the alpha polymorph and the CHCl3 solvate, throwing light on some discrepant results recently appeared in the literature. The thermal behavior of the alpha and beta polymorphs was investigated by coupling thermogravimetric analyses to variable-temperature X-ray powder diffraction experiments. No temperature-stimulated phase transformation could be detected between the two polymorphs, each preserving its structural features up to decomposition, suggesting that kinetic, more than thermodynamic, factors regulate their isolation
Novel Coordination Polymers Based on Bis- and Tris-pyrazolyl Ligands
No full textSeveral pyrazole-based ligands of both rigid and flexible nature have been exploited for the preparation of multifunctional coordination polymers with assorted dimensionality (from 1D to 3D) through either conventional synthetic procedures or solvothermal routes. They were found to display permanent microporosity and remarkable thermal resistance. They were successfully exploited for CO2 adsorption and as solid-state photoluminescence materials
EUCHEME, EUropean CHemists for Energy, Materials and Environment. Intensive Programme 2nd edition (IP) Lifelong Learning Programme Erasmus
No full textThe main objective of the course is to provide a comprehensive and balanced overview of the most important aspects of different subjects (energy and materials production, fine chemicals, environment) related to organometallic chemistry, catalysis, advanced materials, green and environmental chemistry, bridging the gap between the need of advanced training and the actual offer in this field
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